The film thickness of a dielectric gate insulation film is largely influenced by the performance of a MOS transistor, and it is essential that the interface with the silicon substrate is electrically smooth and that the mobility of the carrier does not deteriorate.
Conventionally, a SiO2 film has been used as this gate insulation film, and was the most superior in terms of interfacial quality. In addition, there is a characteristic in that the thinner the SiO2 film used as this gate insulation film, the number of carriers (that is, electrons or electron holes) increases, and the source-drain current also increases thereby.
From the foregoing circumstances, each time the power supply voltage would decrease as a result of miniaturizing the wiring, the gate SiO2 film has been consistently formed as thin as possible within a range that would not deteriorate the reliability of dielectric breakdown. Nevertheless, a tunnel leakage current flows directly when the gate SiO2 film is formed of a thickness of 3 nm or less, and a problem arises in that this film would not function as an insulation film.
Meanwhile, although attempts are being made to miniaturize the transistor, so as long as there are limitations in the film thickness of the SiO2 film, which is the gate insulation film as described above, miniaturization of the transistor loses its significance, and a problem arises in that the performance is not improved.
Moreover, in order to lower the power supply voltage of the LSI as well as lower the power consumption, it is necessary to make the gate insulation film even thinner. Nevertheless, since there is a problem regarding the gate dielectric breakdown when the film thickness of the SiO2 film is made 3 nm or less as described above, thinning of the film had a limitation in itself.
In light of the foregoing circumstances, a high dielectric gate insulation film is being considered lately as a substitute for the SiO2 film. And, the HfSiO film and HfSiON film are attracting attention as this type of high dielectric gate insulation film.
This high dielectric gate insulation film is capable of acquiring, with a comparatively thick film, a capacity equivalent to the SiO2 film, and is characterized in that it is able to suppress the tunnel leakage current. Further, since this can be deemed as a film in which SiO2 or SiOn is added to Hf, interfacial quality similar to that of SiO2 can be expected.
Thus, sought is a sputtering target capable of easily and stably forming a high-grade HfSiO and HfSiON high dielectric gate insulation film.